Integrated Circuit Devices (xe2x80x9cICsxe2x80x9d) are externally connected to IC packages through pads on the IC die. The pads comprise a mechanical contact site and associated circuitry to drive output signals and receive input signals. The technical specifications for the IC typically include minimum parameters of which the IC is capable of providing. One such parameter is the amount of current a driver circuit is able to source when it drives a high value and sink when it drives a low value. Test and measurement of the current capacity parameter typically involves use of an ammeter. An ammeter is often available as part of Automated Test Equipment (xe2x80x9cATExe2x80x9d) that is conventionally used to test ICs. Use of the ammeter on the ATE requires direct connection between an ATE tester channel and the pad of the IC.
As ICs become larger and have more pads and associated circuitry to test, the commensurate ATE that has sufficient test channel capacity to connect a channel to each and every pad becomes quite expensive. A larger IC, therefore, requires a significantly larger capital outlay in order to test it using conventional techniques. An alternative to purchase of a larger ATE for testing larger ICs is selective test of some, but not all, of the pads. This alternative disadvantageously leaves certain IC specifications unverified and produces a costly risk of not identifying a faulty IC.
There is a need, therefore, to address the foregoing deficiencies of the prior art by testing a larger number of IC pads without requiring additional dedicated tester channels.
A method of testing current sourcing or sinking capability of a driver in an IC calls for positioning a charge storage element at an output of the driver and forcing it to a known voltage value. A pulse of known duration and voltage level is applied to a tri-state control input of the driver and a resulting voltage value is measured at the output of the driver. A current flow through the driver is determined to be within testing limits by comparing an expected voltage value against the resulting voltage value.
According to another aspect of the present invention, an apparatus for testing current sourcing or sinking capability of a driver circuit in an IC has the driver circuit with a charge storage element of known capacitive value at an output of the driver circuit. An input circuit permits application of a test pulse of known duration and data input values to the driver circuit. A receiver accepts an output of the driver for determining a threshold voltage value at the driver output.
According to another aspect of a method for testing a driver output circuit according to the teachings of the present invention, an expected resulting voltage value of a charge storage element after application of a discharge pulse of known voltage and duration is calculated. A known charge is stored onto the charge storage element. The driver output circuit is placed in a tri-state condition and the discharge pulse is applied to the driver. A resulting voltage value of the charge storage element is determined to be greater than or less than the expected resulting voltage value.
According to these and other aspects of the present invention, an interface channel of an IC contains elements that make it possible to test current sourcing and current sinking capacity of the interface channel driver without use of a dedicated ATE channel. Advantageously, it is possible to more fully test aspects of an IC with a large number of driver circuits without requiring investment into ATE with a similarly large number of ATE channels.